Jefferson Lab is headed toward new scientific questions - the ones being turned up in the dynamic
research process now going on. Answering them will require even better particle-detection and
data-acquisition technology. This second generation of CEBAF science will also require upgrading
the accelerator to 12 GeV, double the present energy.

A prototype seven-cell superconducting accelerating cavity. Each present cavity has
five cells. All cryomodules contain eight cavities each. Cavities in the new cryomodules will
look like this one.

The 12 GeV CEBAF will enable a major new scientific initiative in meson spectroscopy, a technique
for investigating how quark-antiquark pairs hold together. The upgraded accelerator will also help
reveal the quark substructure of nuclei through deep inelastic scattering experiments, involving
larger transfers of energy as quarks deflect electrons inside target nuclei. Higher energy in CEBAF
will mean sharper views into nuclei, just like increasing a microscope's magnification. That's why
the nation's Nuclear Science Advisory Committee and the National Academy of Sciences endorse the
upgrade's scientific opportunities.

Increasing the energy means improving the accelerating cavities and building the upgraded cryomodules
that will contain them - ten cryomodules to be added to the accelerator outright, and, depending on
performance, up to six more to replace some of the present ones. The new seven-cell cavities in the
upgraded cryomodules will have higher gradient, boosting the beam's energy faster within a given length.
They will also operate with a better Q, or quality factor, reducing power consumption and cost.

Together with constructing a fourth experimental hall, Hall D, the upgrade also requires increasing the
fields in the magnets that transport the beam, adding a tenth beam-recirculation arc between the two
linacs (linear accelerators), and doubling the capacity of the central helium refrigeration plant.
(The accelerating cavities can operate superconductively because they are immersed in liquid helium at
2 degrees Kelvin, some 456 degrees Fahrenheit below zero.)

When CEBAF was originally planned for 4 GeV, its designers, mindful of the future, made sure to accommodate
the possibility of future upgrades. That same principle will apply in 12 GeV preparations. In the still
longer term, the energy might well be doubled yet again, to 24 GeV - for a third generation of Jefferson Lab science.